CdHgTe photodiodes array

Abstract

A photodiodes array includes a useful layer made of Cd x Hg 1-x Te; first doped zones each forming a PN junction with a second doped zone surrounding the first doped zones. The array includes regions located between two PN junctions, with a cadmium concentration gradient decreasing from the upper face to the lower face of the useful layer. A method of making such a photodiodes array includes producing, on the upper face of the useful layer, of a structured layer with at least one through opening, and with a cadmium concentration higher than the cadmium concentration in the useful layer; annealing the useful layer covered by the structured layer, with diffusion of cadmium atoms of the structured layer, from the structured layer to the useful layer; producing at least two PN junctions in the useful layer.

The invention claimed is: 
     
       1. A photodiodes array comprising:
 a useful layer made of a semiconducting alloy of cadmium, mercury and tellurium of the Cd x Hg 1-x Te type, the useful layer having an upper face and a lower face; 
 at least two first doped zones, located in the useful layer, each forming a PN junction with a second doped zone surrounding the first doped zones, the PN junctions being flush with the upper face of the useful layer; 
 wherein the array comprises at least one region, located between two neighbouring PN junctions, and has a cadmium concentration gradient decreasing from the upper face to the lower face of the useful layer. 
 
     
     
       2. The array according to  claim 1 , wherein the average concentration of cadmium in said region is higher than the average concentration of cadmium in the remainder of the useful layer. 
     
     
       3. The array according to  claim 1 , wherein said region extends between two PN junctions, and outside each first doped zone. 
     
     
       4. The array according to  claim 3 , wherein said region extends in the useful layer deeper than the first doped zones. 
     
     
       5. The array according to  claim 1 , wherein said region extends between two PN junctions, and in an upper peripheral volume of each of the first doped zones. 
     
     
       6. The array according to  claim 5 , wherein said region extends in the useful layer less deep than the first doped zones. 
     
     
       7. The array according to  claim 5 , wherein said region extends in a first doped zone over less than half of the volume of this first doped zone. 
     
     
       8. The array according to  claim 1 , wherein said region has:
 a first portion extending outside the first doped zones; and 
 a second portion extending in an upper peripheral volume of at least one first doped zone; 
 the first portion extending deeper in the useful layer than the second portion, and the first portion being surrounded by the second portion. 
 
     
     
       9. The array according to  claim 1 , wherein the first doped zone is P-doped by arsenic atoms. 
     
     
       10. A method of fabrication of a photodiodes array according to  claim 1 , comprises the following steps:
 producing, on the upper face of the useful layer, a structured layer with at least one through opening, and with a cadmium concentration higher than the cadmium concentration in the useful layer; 
 annealing of the useful layer covered by the structured layer, with diffusion of cadmium atoms of the structured layer, from the structured layer to the useful layer; 
 producing at least two PN junctions in the useful layer. 
 
     
     
       11. The method according to  claim 10 , wherein the production of a structured layer involves:
 depositing of a reservoir layer on the upper face of the useful layer; and 
 etching of at least one through opening in the reservoir layer, the etching being a chemical etching. 
 
     
     
       12. The method according to  claim 10 , wherein the steps of production of a structured layer and annealing form a fabrication cycle, and at least two fabrication cycles are implemented. 
     
     
       13. The method according to  claim 10 , wherein the step of production of the PN junctions make use of an arsenic ion implantation. 
     
     
       14. The method according to  claim 10 , wherein annealing is done at a temperature of between 100° C. and 500° C. 
     
     
       15. The method according to  claim 14 , wherein annealing is done for a duration of between 1 hour and 100 hours.